Donald Redfield Griffin (1915-2003) was an American professor of zoology at various universities who did seminal research in animal behavior, animal navigation, acoustic orientation and sensory biophysics.
In the Preface to this 1992 book, Griffin states, "This book will review evidence of versatile thinking by animals, and of equal significance will be a representative sampling of the wide range of scientific and scholarly opinion about animal minds. This spectrum of strongly advocated views demonstrates the basic importance attached to the nature of animal mentality by both scientists and philosophers." In the first chapter, he elaborates, "The aim of this book is to reopen the basic question of what life is like, subjectively, to nonhuman animals, and to outline how we can begin to answer this challenging question by analyzing the versatility of animal behavior, especially the communicative signals by which animals sometimes appear to express their thoughts and feelings."
He points out that "Adaptiveness is a completely separate matter from the possibility of conscious thinking. Because mantis shrimp are crustaceans a few centimeters in length, it is assumed a priori that they cannot possibly be conscious." (pg. 200) After reviewing the various "Ape Language" experiments, he says, "On balance, it now seems clear that apes have learned to communicate simple thoughts."
He concludes on the note, "I am confident that with patience and critical investigation we can begin to discern what life is like, subjectively, to particular animals under specific conditions.... Because mentality is one of the most important capabilities that distinguishes living animals from the rest of the known universe, seeming to understand animal minds is even more exciting and significant than elaborating our picture of inclusive fitness or discovering new molecular mechanisms."